Hydrodealkylation of special feed stocks



United States Patent 3,145,238 HYDRODEALKYLATION 0F SPECIAL FEED STGCKSWilliam Newton Kestner, Baton Rouge, La., assignor to Ease Research andEngineering Company, a corporation of Delaware No Drawing. Filed June19, 1961, Ser. No. 117,808 7 Claims. (Cl. 260-672) The present inventionrelates to a combined steam cracking and hydrodealkylation process foreconomically producing both the ordinary olefins and diolefins obtainedconventionally from high conversion steam cracking, and pure aromaticmaterials, e.g. naphthalene. More particularly, this invention relatesto steam cracking heavy virgin crude oils or selected fractions of theproducts from catalytic cracking e.g. light catalytic cycle oil undersevere conditions to crack substantially all of the paraffins presentand feeding the aromatic concentrate so prepared to hydrodealkylation toprepare e.g. naphthalene and also small amounts of benzene. Mostparticularly, in a preferred embodiment, this invention relates in sucha process to severely steam cracking such feeds boiling in the range of400 to 650 F. under conditions to obtain 25 to 45 wt. percentconversions to C materials.

Process for the hydrodealkylation of alkyl substituted aromaticcompounds are well-known and widely used at the present time. Theseprocesses are both of the thermal non-catalytic type and of thecatalytic type, e.g. utilizing a chromia on alumina catalyst. Apreferred method for carrying out the thermal non-catalytichydrodealkylation is described in S.N. 91,832, filed February 27, 1961.In all of these processes hydrodealkylation is obtained with aconsumption of at least 1 mole of hydrogen per alkyl group due to thebreaking off of the alkyl side chain to form the aromatic compound and asaturated aliphatic parafiin. Feed stocks for these processes are, ofcourse, conventionally obtained from crude oil, catalytic reformate,catalytic cycle oils, etc. which have been extracted to concentrate thearomatic fraction. Thus, in the hydrodealkylation process it isordinarily necessary to extract to limit the amount of parafiins andolefins present which otherwise are cracked to predominantly methanewith the consumption of large amounts of hydrogen. This is undesirablein that expensive hydrogen is consumed to form cheap products of smallsales value.

It has now surprisingly been discovered that excellent feed stocks forhydrodealkylation may be obtained by steam cracking at high conversionsspecific feed stocks to thus obtain not only the conventional olefinsand diolefins obtained from steam cracking but also superior naphthaleneprecursors to those obtained from conventional S0 phenol, etc.extraction. Thus, in these extraction processes the extract containsconsiderable non-aromatic material as side chains. In steam crackingvaluable olefins and diolefins are made from the fracture of thearomatic side chains as well as from the non-aromatic portion of feedstocks. This is compared with the cheap methane produced and highhydrogen consumption which would be obtained if an extraction processwere used to concentrate the aromatics. An additional advantage of thepresent process is that desulfurization prior to steam cracking may beused without detriment since the tetralins so formed are dehydrogenatedback to alkyl naphthalenes in the steam cracking step. Thus, it is knownthat alkyl naphthalenes give considerably higher selectivities to thedesired naphthalene in hydrodealkylation.

Preferred feed stocks to be fed to steam cracking according to thisinvention boil in the range of 300 to 800 F. These feed stocks containalkyl naphthalene, naphthalene, alkyl tetralins, alkyl benzenes,paraflins and small amounts of olefins. Preferred aromatic hydrocarbonfeeds are suitably obtained from crude petroleum from catalytic crackingand less preferably from catalytic reforming.

Preferred feed stocks from catalytic cracking boil in the range of 400to 850 F., preferably 430 to 590 F., e.g. 430 to 560 F.; and contain 15to 30 wt. percent, preferably 20 to 30 wt. percent, e.g. 30 wt. percentnaphthalenes and alkyl naphthalenes; 2 to 6 wt. percent, preferably 4 to6 wt. percent, e.g. 6 wt. percent alkyl tetralins; 3 to 24 wt. percent,preferably 10 to 24 wt. percent, e.g. 24 wt. percent, alkyl benzenes;and 40 to 80 wt. percent, preferably 40 to 60 wt. percent, e.g. w-t.percent parafiins and olefins. A description of a preferred catalyticcracking process is contained in U.S. 2,589,124. Preferred feeds to saidcatalytic cracking process boil in the range of 475 to 1050 F., e.g. 600to 900 F. to produce feeds for the present process.

From crude oil preferred fractions boil in the range of 300 to 850 F.,preferably 400 to 800 F., e.g. 500 to 750 F.; and contain 8 to 30 wt.percent, preferably 20 to 30 wt. percent, e.g. 30 wt. percent,naphthalenes and alkyl naphthalenes; 4 to 20 wt. percent, preferably 8to 20 wt. percent, e.g. 20 wt. percent alkyl tetralins; 2 to 15 wt.percent, preferably 5 to 15 wt. percent, e.g. 15 wt. percent alkylbenzenes; and 35 to 70 wt. percent, preferably 35 to wt. percent, e.g.35 Wt. percent paraffins and olefins. Preferred crude oils are thosehaving a high aromatic content obtained for example from San Joaquin(Venezuelan) or Tia Juana (Venezuelan) crude or Aramco (Near East)crude.

A less preferred feed stock is obtained from hydroforming, preferablyplatinum hydroforming. These feeds boil in the range of 300 to 700 F.,preferably 400 to 650 F., e.g. 430 to 560 F.; and contain 20 to 40 wt.percent naphthalenes and alkyl naphthalenes; 2 to 6 wt. percent,preferably 4 to 6 wt. percent, e.g. 6 wt. percent, alkyl tetralins; 20to 40 wt. percent, preferably 30 to 40 wt.

percent, e.g. 40 wt. percent alkyl benzenes; and 14 to 50 wt. percent,preferably 14 to 20 wt. percent, e.g. 14 wt. percent, parafiins andolefins. A description of a preferred process for platinum hydroformingis contained in U.S. 2,902,427. Preferred feeds to said platinumhydroforming boil in the range of 300 to 600 F., e.g. 340 to 500 F. toproduce feeds for the present process.

Steam cracking is conducted at temperatures in the range of 1100 to 1500F., preferably 1200 to 1490 F., e.g. 1400 F., pressures of 1 to 20p.s.i.g., preferably 1 to 10 p.s.i.g., e.g. 5 p.s.i.; for residencetimes of .1 to 1.0 second, preferably .1 to .4 second, e.g. .2 second,and utilizing amounts of steam in the range of50 to moles, preferably 60to 80 moles, e.g. 75 moles per moles of feed.

Preferred conversions to C are controlled in the range of 20 to 60 Wt.percent, preferably 25 to 55 wt. percent,

e.g. 35 wt. percent. The products from the steam cracking zone areimmediately quenched and are separated by fractionation to remove thedesired fraction to be fed to the hydrodealkylation reactor. Thisfraction may be a broad cut boiling in the range of 160 to 600 F.,preferably 200 to 590 F., e.g. 220 to 560 F. (used to prepare both e.g.naphthalene and benzene) or alternatively may be a narrow cut containingonly the naphthalene precursors boiling in the range of 400 to 600 Fpreferably 420 to 590 F., e.g. 430 to 560 F. It should be noted that thealkyl benzene material boiling at a lower temperature than thenaphthalene precursors will be valuable either for the separation ofpure components, e.g. ethyl benzene from this fraction or for feeding itseparately or with the naphthalene precursors to hydrodealkylation toproduce benzene.

Hydrodealkylation is conducted at temperatures in the reaction zonecontrolled in the range of 1100 to 1600 F., preferably 1150 to 1400 F.,e.g. 1150 to 1375 F., pressures of 500 to 1000 p.s.i.g., preferably 400to 700 p.s.i.g., e.g. 600 p.s.i.g., and for reaction times of 2 to 120seconds, preferably 2 to 100 seconds, e.g. 50 seconds. Preferably thereaction is carried out in a reaction zone having a high L/ D ratio,preferably 40:1 to 150:1, e.g. 65.1, and utilizing a hydrogen quench tocontrol the temperature of the reactants, all as described in S.N.91,832 filed February 27, 1961. The amount of hydrogen-containing gasinitially supplied is 1 to 6 moles, preferably 2 to 4 moles, e.g. 3moles per mole of the alkyl aromatic material contained in the feed. Thehydrogen-containing gas according to the present invention shouldcontain above 50% hydrogen, preferably above 80%, more preferably above90%, e.g. 92% hydrogen. In a preferred embodiment the amounts ofhydrogen above described are initially supplied and additional amountsof hydrogen are supplied at quench points to control the reactiontemperature in the reaction zone below 1300 F. The amount of additionalhydrogen added in this embodiment is 2 to moles, preferably 3 to 10moles, e.g. 7 moles per mole of aromatic material in the feed. Ingeneral, all the preferred procedures described in S.N. 91,832, filedFebruary 27, 1961, may be used in the present process. Reaction productsfrom the hydrodealkylation reaction are immediately quenched and thedesired pure naphthalene and other aromatic compounds are separated bydistillation.

The present invention will be more clearly understood from aconsideration of specific examples showing preferred methods forcarrying out the present invention.

Example 1 A feed stock boiling in the range of 430 to 600 F. obtainedfrom the catalytic cracking of a 500 to 990 F. gas oil from SouthLouisiana crude is fed to a steam cracker operated under the followingconditions.

Temperatures 1400 F. coil outlet. Pressures 12 p.s.i.g. at coil outlet.Residence times .3 second above 900 F. Amount of steam/100 moles of feed75 moles.

Product gases from the steam cracker after quenching and separation ofwater are fractionated to separate an aromatic concentrate boiling inthe range of 430 to 590 F. This feed is fed to the hydrodealkylationprocess and contains 17 wt. percent parafiins, 13 wt. percent alkylbenzenes, 19 wt. percent indanes, wt. percent alkyl naphthalenes, 3 wt.percent tetralins and 14 wt. percent other aromatics such asacenaphthene and phenanthrene boiling in this range. This feed issupplied with 3.1 moles per mole of feed of a 92% hydrogen stream (theremainder being essentially methane) to a furnace at a temperature of850 F. In this furnace the combined stream is heated to a temperature of1100 F. in approximately 3 seconds. The 1100 F. stream is supplied to aninternally lined 65:1 L/D reactor operating at 600 p.s.i.g.

wherein in the first section the temperature-rises to 1225 F. and isquenched with the same 92% hydrogen-containing gas to a temperature of1150 F. This quench gas is supplied at F., and the amount of the gas is1.5 moles per mole of feed. At the second quench point the temperatureis 1260 F. and 2.2 moles of the hydrogen-containing gas per mole ofhydrocarbon feed (introduced at the same temperature as above) isutilized to cool the reactants to 1160 F. At the third quench point thetemperature is 1310 F. and 3.5 moles of the same hydrogencontaining gasper mole of hydrocarbon feed, again at the same temperature, is used tocool the reactants to a temperature of 1160 F. The final quench is withrecycle gas from the process without hydrogen enrichment containing 60mole percent hydrogen, the remainder being light hydrocarbons andprincipally methane. This gas is supplied at a temperature of 100 F. andthe amount of the final quench gas is 4.4 moles per mole of reactants.This quench rapidly cools the gases to a temperature of 1150 F. Theapproximate vapor velocity in the reactor varies from 1.5 at the inletto 4.5 feet/second at the outlet and the contact time is about 50seconds. For these conditions, about 95% of the alkyl aromatics aredealkylated into the desired product of benzene and naphthalene.

Example 2 A feed stock boiling from 420 to 589 F. obtained from thecatalytic cracking of a 490 to 1050 F. gas oil from a mixture of SouthLouisiana, North Louisiana and Louisiana-Mississippi crudes was fed to asteam cracker operating under the following conditions.

Temperature 1420 F. coil outlet. Pressure 10.8 p.s.i.g. at coil outlet.Residence time 0.25 second above 900 F. Amount of steam 77 mole percenton feed.

Product gases from the steam cracker after quenching and separation ofwater were fractionated to separate an aromatic concentrate boiling from424 to 579 F. The yield of this material was 17.4 Wt. percent on steamcracking feed.

It is to be understood that this invention is not limited to thespecific examples, which have been offered merely as illustrations, andthat modifications may be made without departing from the spirit of thisinvention.

What is claimed is:

1. The combined steam cracking and hydrodealkylation process whichcomprises steam cracking at high conversions a product stream fromcatalytic cracking boiling in the range of 300 to 850 F., distilling thereaction products from the said steam cracking to separate an aromaticconcentrate fraction boiling within the range of to 600 F.,hydrodealkylating the said aromatic concentrate fraction at temperaturesin the range of 1100 to 1600 F., and separating a dealkylated aromaticfrom the reaction products from the said hydrodealkylation.

2. The process of claim 1 in which steam cracking is carried out atseverities to obtain C conversions of 20 to 60 wt. percent.

3. The process of claim 1 in which the feed stock is an oil obtainedfrom the products from catalytic cracking of a gas oil boiling in therange of 475 to 1050 F., the said oil being a fraction selected withinthe boiling range of 400 to 850 F.

4. The process of claim 1 in which the product stream from catalyticcracking is obtained from a catalytic cracking process in which a partof this product stream is recycled in the catalytic cracking operation.

5. The process of claim 1 in which hydrodealkylation is carried outthermally in the absence of a catalyst at temperatures in the range of1150 to 1400" F.

6. The process of claim 1 in which the aromatic concentrate fraction isa fraction selected within the boiling range of 160 to 600 F.

7. The combined steam cracking and hydrodealkylation 3,145,238 5 5processwhich comprises steam cracking at high converin a reaction zonehaving an L/D ratio in the range of sions to C in the range of 25 to 55Wt. percent a 40:1 to 150:1 and separating adealkylated aromatic fromProduct Stream from l/ Cracking boiling Within the the reaction productsfrom the said hydrodealkylation. range of 430 to 590 F., distilling thereaction products from the said steam cracking to separate an aromaticfrac- 5 References Cited in the file of this patent tion boiling Withinthe range of 420 to 590 F., hydrodealkylating the said aromaticconcentrate fraction at UNITED STATES PATENTS temperatures in the rangeof 1150 to 1400 F., pressures 9 Welty July 10, 1945 of 400 to 700p.s.i.g. for reaction times of 2 to 100 seconds 2,431,515 h p r on N V.Q5, 1947

1. THE COMBINED STEAM CRACKKNG AND HYDRODEALKYLATION PROCESS WHICHCOMPRISES STEAM CRACKING AT HIGH CONVERSIONS A PRODUCT STREAM FROMCATALYTIC CRACKING BOILING IN THE RANGE OF 300 TO 850*F., DISTILLING THEREACTION AROMATIC CONCENTRATE FRACTION BOILING WITHIN THE RANGE OF 160TO 600*F., HYDRODEALKYLATING THE SAID AROMATIC CONCENTRATE FRACTION ATTEMPERATURES IN THE RANGE OF 1100 TO 1600*F., AND SEPARATING ADEALKYLATED AROMATIC FROM THE REACTION PRODUCTS FROM THE SAIDHYDRODEALKYLATION.